Pet-food tainting raises safety questions Q&A: What's melamine? And how does it affect humans and animals?The Associated PressUpdated: 7:15 p.m. ET April 25, 2007First, cats and dogs were sickened and died after they ate pet food contaminated with an industrial chemical. Then, it was disclosed that hogs were fed the same pet food, raising concerns that the chemical had entered the human food supply.

Some questions and answers about the contamination, the massive recall that followed and the risks to people and animals:

Q: What chemical tainted the food?

A: Traces of melamine, a nitrogen-rich chemical used in a variety of industrial processes, were found in the pet food. Its most common use is to make resins, which in turn can be molded into products like countertops and kitchen utensils, including plastic dinnerware sold as Melmac. It also is both a contaminant and byproduct of several pesticides, including cyromazine, according to the Environmental Protection Agency.

Q: Is melamine toxic to animals?

A: Melamine appears to have caused acute kidney failure in animals that have died or been sickened after eating foods laced with the chemical. Previously, the only known risk was to rodents. When fed to male rats in high doses, melamine indirectly caused tumors by forming stones that irritated the lining of the bladder, according to a 2002 United Nations Environmental Program report. The report concluded its toxicity to mammals is low.

Q: How many pets have died after eating contaminated food?

A: No one knows. Estimates run from a few dozen to several thousand dogs and cats. The FDA has confirmed only about 15 pet deaths.

Q: What about people?

A: The 2002 UN report concluded the potential risk posed by melamine is low. However, the UN based that conclusion on the slim chance that consumers would even come into contact with the chemical.

Q: Has melamine been found in any human foods?

A: No. However, the FDA is beginning to test wheat gluten, rice protein concentrate and at least four other vegetable proteins imported for use by firms that make human food, including pizza dough and infant formula, and those that manufacture animal feed.

Q: Whatís the connection to human food?

A: State and federal investigators are looking at hog farms in at least six states that were supplied with salvaged pet food distributed before it was known to be contaminated with melamine. It wasnít immediately clear which farms had hogs that actually ate the contaminated pet food, though the urine of animals has tested positive for the chemical in California, North Carolina and South Carolina. Some hog farms have been placed under quarantine. A poultry farm in Missouri also may have received some tainted food.

Q: How many brands of pet food were recalled?

A: Companies have recalled more than 5,500 varieties of pet food and treats, sold under more than 100 brands.

Q: What advice has FDA given pet owners?

A: The agency recommends checking if a petís food has been recalled. Any recalled food should not be used. A complete, searchable list is available on the FDAís Web site. If a pet suffers a loss of appetite, lethargy or vomiting, the FDA suggests owners contact a veterinarian.

Q: How did the melamine get into the pet food in the first place?

A: Two vegetable proteins tainted with melamine were imported from China and used in pet foods sold in North America, while a third was used in southern Africa. In the United States, melamine has shown up in wheat gluten and rice protein concentrate. The protein-rich ingredients were used to produce the now-recalled brands of pet foods and treats by U.S. and Canadian companies. And in pet products sold in South Africa and Namibia, the third vegetable protein ingredient, corn gluten, also has been found to be contaminated.

Q: Why would melamine show up in those ingredients?

A: The Food and Drug Administration suspects melamine was used to spike the vegetable proteins to make them appear to have more protein than they actually did. Adding a nitrogen-rich contaminant like melamine would skew the results of tests to make an ingredient register as more protein-rich than it really is ó and allow it to sell for more money.

Q: Who imported the tainted ingredients and where did they go?

A: All three vegetable proteins tainted with melamine were imported from China. Two companies are known to have imported tainted ingredients: ChemNutra Inc. of Las Vegas bought wheat gluten, and Wilbur-Ellis Co. of San Francisco purchased the rice protein concentrate. Both companies in turn sold the wheat gluten and rice protein concentrate to pet food manufacturers or distributors that supply such companies. The FDA does not believe either ingredient went directly to any company that used them to make human food.

Q: Why werenít the ingredients tested for melamine?

A: Until the recent and ongoing recalls, regulators did not consider melamine a likely contaminant of food meant for either people or animals. Nor were the vegetable proteins considered at risk for contamination. The FDA is now testing a variety of vegetable proteins, used to make everything from infant formula to energy bars, for the chemical.

Q: What else is the government doing to ensure the safety of the food people and pets eat?

A: The FDA is inspecting factories and warehouses and analyzing both raw ingredients and finished pet foods as part of its efforts to track down all the contaminated product. Agency inspectors also plan to visit plants in China where the suspect ingredients were made. Along with the USDA and state officials, the FDA is investigating cases where contaminated pet food was fed to hogs and poultry. The FDA is also fielding consumer complaints as well as calls from veterinarians. And agency criminal investigators continue to monitor the situation.

Q: What about Congress?

A: Lawmakers have begun a series of investigations into how the FDA polices the safety of the nationís food supply. Legislative proposals include the creation of a single food agency. Sen. Tom Harkin, D-Iowa, has called for an audit of the nationís food safety system. Rep. Rosa DeLauro, D-Conn., has said that unless the FDA improves how it handles food safety investigations she would seek to withhold the paychecks of top agency officials.